Charset for database connection is always UTF-8

node-firebird doesn't let you choose the charset connection, it will always use UTF-8.
Node is unicode, no matter if your database is using another charset to store string or blob, Firebird will transliterate automatically.

This is why you should use Firebird 2.5 server at least.

Firebird 3.0 Support

Firebird new wire protocol is not supported yet so
for Firebird 3.0 you need to add the following in firebird.conf